Low-dose methotrexate is ineffective in primary biliary cirrhosis: long-term results of a placebo-controlled trial

BACKGROUND & AIMS

New treatments for primary biliary cirrhosis (PBC) need to be evaluated. We conducted a single-center double-blind, randomized trial of methotrexate, 7.5 mg/wk (n = 30), vs. placebo (n = 30) for up to 6 years in PBC.

METHODS

Methods included three monthly symptom assessment and liver function tests and liver biopsy and gastroscopy at baseline, after 2 years, and after 4-6 years.

RESULTS

Patients randomized to methotrexate had, compared with patients randomized to placebo, (1) significantly lower on-treatment serum alkaline phosphatase, gamma-glutamyltransferase, immunoglobulin (Ig) M, IgG, and (after 24 months) aspartate aminotransferase and alanine aminotransferase levels (P < 0.02-0.001 by analysis of covariance to adjust for baseline differences); (2) a nonsignificant trend toward lower on-treatment pruritus scores; (3) similar on-treatment Knodell inflammatory scores but nonsignificant trends toward lower Knodell fibrosis score and less ductopenia; (4) a trend toward greater increases in serum bilirubin level and Mayo score with time (both significant after 5 years of follow-up); and (5) a 2.9-fold (95% confidence interval, 0.85-10.25-fold) increase the rate of death or liver transplantation as a result of liver disease during or after the trial (P = 0.09) in a Cox multivariate regression analysis compared with patients randomized to placebo.

CONCLUSIONS

These results do not support the clinical use of low-dose methotrexate in PBC.

A soluble major histocompatibility complex class I peptide-binding platform undergoes a conformational change in response to peptide epitopes

Class I major histocompatibility complexes (MHC) are heterotrimeric structures comprising heavy chains (HC), beta2-microglobulin (beta2-m), and short antigenic peptides of 8-10 amino acids. These components assemble in the endoplasmic reticulum and are released to the cell surface only when a peptide of the appropriate length and sequence is incorporated into the structure. The binding of beta2-m and peptide to HC is cooperative, and there is indirect evidence that the formation of a stable heterotrimer from an unstable HC:beta2-m heterodimer involves a peptide-induced conformational change in the HC. Such a conformational change could ensure both a strong interaction between the three components and also signal the release of stably assembled class I MHC molecules from the endoplasmic reticulum. A peptide-induced conformational change in HC has been demonstrated in cell lysates lacking beta2-m to which synthetic peptides were added. Many features of this conformational change suggest that it may be physiologically relevant. In an attempt to study the peptide-induced conformational change in detail we have expressed a soluble, truncated form of the mouse H-2Db HC that contains only the peptide binding domains of the class I molecule. We have shown that this peptide-binding "platform" is relatively stable in physiological buffers and undergoes a conformational change that is detectable with antibodies, in response to synthetic peptides. We also show that the structural features of peptides that induce this conformational change in the platform are the same as those required to observe the conformational change in full-length HC. In this respect, therefore, the HC alpha1 and alpha2 domains, which together form the peptide binding site of class I MHC, are able to act independently of the rest of the molecule.

A human macrophage-associated antigen (CD68) detected by six different monoclonal antibodies

Antibodies grouped together by the Third Workshop on Leucocyte Differentiation Antigens on the basis of pan-macrophage reactivity on tissue sections were analysed in immunoprecipitation experiments. Antibodies Y2/131, EBM11, Ki-M6 and Ki-M7 all precipitated antigens of Mr 110,000 which were shown to be identical by preclearing experiments. In addition a recently produced antibody, KP1, which identifies macrophages in paraffin-embedded tissue, was shown to recognize the same antigen. The antibodies were tested on murine cells transfected with two clones, which had been isolated by screening a cDNA library with antibodies Y1/82A and EBM11. Cells transfected with the longer cDNA clone, coding for a molecule of Mr 110,000, reacted with antibodies Y2/131, EBM11, Y1/82A and Ki-M6, whilst the shorter clone, encoding a molecule of Mr 70,000 gave the same result except that it did not induce expression of the Ki-M6 epitope. KP1 antibody did not recognize any transfectants, possibly because of differences in glycosylation by the transfected cell line compared with human tissue. Five of the six antibodies appear to recognize different epitopes (the sixth, Ki-M7, not having been evaluated in this way). It was concluded that these six antibodies react with a macrophage-associated antigen for which the gene has been cloned. This group of antibodies has recently been designated CD68 by the Fourth Workshop on Human Leucocyte Differentiation Antigens.

The kinetics of ox kidney biliverdin reductase in the pre-steady state. Evidence that the dissociation of bilirubin is the rate-determining step

When the production of bilirubin by biliverdin reductase was monitored at 460 nm by stopped-flow spectrophotometry a 'burst' was observed with a first-order rate constant at pH 8 of 20 s-1. The steady-state rate was established on completion of the 'burst'. When the reaction was monitored at 401 nm there was no observed steady-state rate, but a diminished pre-steady-state 'burst' reaction was still seen with a rate constant of 22 s-1. We argue that the rate-limiting reaction is the dissociation of bilirubin from an enzyme.NADP+.bilirubin complex. With NADPH as the cofactor the hydride-transfer step was shown to exhibit pH-dependence associated with an ionizing group with a pK of 7.2. The kinetics of NADPH binding to the enzyme at pH 7.0 were measured by monitoring the quenching of protein fluorescence on binding the coenzyme.

The reaction mechanism of bovine kidney biliverdin reductase

The steady-state kinetics of biliverdin reductase can be studied in detail at pH 9 as under these conditions the Km for biliverdin is high enough to obtain reliable measurements of the initial rate in the absence of any biliverdin binding proteins. The initial rate kinetics and the product-inhibition studies are consistent with an ordered sequential mechanism provided the biliverdin concentration was below 20 microM. Above this concentration significant flux occurs through a substrate inhibition pathway involving an enzyme-NAD(P)-biliverdin complex. Chloride is shown to cause a significant activation of the enzyme under certain conditions and this is shown to result from an inability of biliverdin to bind to an enzyme-NAD-chloride complex.